The present invention relates to the field of angular velocity measurement sensors. Specifically, a magnetohydrodynamic angular rate sensor is described for sensing low frequency angular velocities.
As described in U.S. Pat. No. 4,718,276, it is possible to measure angular velocity about an axis of rotation using MHD angular rate sensors. These prior art sensors employ an annulus of liquid mercury which functions as a passive inertial proof mass. As the sensor having the annulus of liquid mercury rotates about a measurement axis, the relative motion between the liquid mercury proof mass and the channel within which the liquid mercury is maintained results in a voltage potential difference across the channel. A permanent magnet supplies the requisite magnetic field to generate the electric voltage orthogonally oriented to the magnetic flux across the mercury channel.
When using the sensors in applications which require the measurement of low frequency angular motion, the sensors have a limited sensitivity at a frequency of less than 10 Hz. Thus, the frequency response falls off rapidly below 10 Hz, providing uncertainty for angular velocity measurements below 10 Hz. It is with this limitation that the present invention finds its particular utility.
In applications in which it is desired to measure such low frequency angular velocity, angular rate gyroscopes are frequently used. The gyroscopes have a limited life due to mechanical wear and fatigue of the complicated movable component systems.
The present invention is therefore provided to measure the low frequency angular measurements heretofore unattainable by the magnetohydrodynamic angular rate sensors of the prior art, and provide sensors which are less susceptible to mechanical wear and fatigue.